The method and apparatus of the invention may be used for the cutting of many types of sheet material where the sheets are irregular insofar as having different sizes and shapes and/or faults or areas of differing quality the number and location of which occur randomly in different pieces. Perhaps the most common application to which the invention may be put is the cutting of hides to produce parts for automobile upholstery, furniture upholstery, shoes and other leather articles. Therefore for convenience, the invention is hereinafter described and claimed with the term "hide" being used to refer to each work piece in question. It is to be understood however that there is no intention in doing so to limit the invention to work pieces produced from animal skins, but instead it is intended that the invention embrace use of the claimed method and apparatus with other irregular work pieces as well.
In the case of hides produced from animal skins, the hides not only vary in size and shape from one another, but also often contain faults such as scars, holes or scratches, or areas of differing thickness, texture or other quality peculiar to each hide. Therefore, without a large wastage of material it is usually impossible to cut a standard selection and arrangement of quality parts from each hide. Instead, it is common practice preparatory to the cutting of a hide to compare it with patterns representing desired parts and to select and move such patterns over the surface of the hide until an acceptable arrangement of the patterns on the hide is obtained. A record of this acceptable arrangement of part patterns is then made in some way for later use in cutting parts corresponding to the patterns from the hide. This record may take various different forms and is hereinafter referred to as a "marker".
Another problem in the cutting of hides is that since the hides are of limited size, when a large number of parts is desired it is necessary to cut them from a number of individual hides, and in the past it has been difficult to achieve an efficient assignment of particular ones of the desired parts to different hides and to arrange the parts assigned to each hide in an efficient way reducing material wastage.
Also, when the desired parts consist mainly of relatively large parts, such as is generally the case, for example, when making parts for automobile upholstery, it is often difficult or impossible to arrange part patterns on a hide without leaving large areas of waste material from which smaller parts, such as parts for watch straps or wallets, for other jobs might be cut if some practical way were available for including such parts in the marker created for each hide.
The general object of the invention is therefore to provide a method and apparatus whereby the above-mentioned problems are solved to produce a highly efficient utilization of hides in the cutting of parts therefrom with a minimum of labor being required. As part of the solution of this object the invention involves a method and apparatus wherein a plurality of hides are first digitized to produce a computer memory stored record of their shapes and sizes and other surface features of interest such as the locations and sizes and shapes of faults and areas of differing quality. After a substantial stock of digitized hides has been produced, information defining a set of desired parts is supplied to a computer which then either automatically or through interaction with a human operator makes an efficient selection of hides from the digitized stock and produces a marker for each selected hide containing an efficient selection and arrangement of parts to be cut from that hide.
A practical carrying out of this procedure involves first digitizing a supply of hides and then holding them in storage remote from the digitizing table until selected ones are called up for cutting. This requires that each hide be spread once for digitizing and be spread again for cutting. In doing this, however, it is most important that the hide when spread for cutting have precisely the same shape as it had when spread for digitizing and that it have a location on the supporting surface of the cutter bearing a known relationship to its location on the supporting surface of the digitizer. During both the digitizing process and the cutting process it is also desirable that the hide be held quite flatly against the support surface so as to avoid wrinkles, raised bumps and other departures from a flat surface. Hides, however, are generally relatively flexible and shiftable in plane so that if a hide is casually spread two times the shape it assumes the second time may depart significantly from the shape it assumed the first time. For example, if in the second spreading two points of the hide for reference purposes are taken to have locations exactly corresponding with the locations of those points assumed during the first spreading, other points of the hide may depart by as much as an inch or more from the locations assumed during the first spreading.
A further object of the invention is therefore to include in the method and apparatus of the invention a way of assuring that a hide when spread for cutting will have a shape very closely corresponding to the shape assumed when spread for digitizing, thereby allowing the production and use of efficiently laid out markers for the hides without danger of cutting unacceptable parts because of the hide having a different shape when cut than when digitized.
A still further object of the invention is to provide a method and apparatus of the aforegoing character wherein each hide is held in a desirable flat condition both during digitizing and cutting.
Other objects and advantages of the invention will be apparent from the following description and claims and from the accompanying drawings.